This application relates to a lamp assembly, and more particularly a combined lamp assembly incorporating a fluorescent lamp and more preferably a compact fluorescent lamp (CFL) light source and at least one light emitting diode (LED) light source. More particularly, this application relates to a combined arrangement for operating the lamp assembly, and particularly a combined driver circuit for the two light sources. However, it will be appreciated that the disclosure may find use in related environments and applications.
It is generally known to provide a lamp assembly having combined light sources. For example, different types of light sources may be combined in a lamp assembly where each light source provides a different type of light output, and the combined output provides a mixture of light that cannot be achieved by either light source on its own. Commonly owned and co-pending application (U.S. Ser. No. 12/021,880, filed 29 Jan. 2008) discloses a combined lamp assembly that includes a CFL light source and at least one LED light source and the disclosure thereof is expressly incorporated herein by reference. Particularly, the LED is preferably one that emits red light. The red light of the LED is mixed with the output of the CFL to advantageously provide an enriched, red color to the combined light output.
Known lamp assemblies that combine light sources usually employ separate, first and second driver circuits, namely a dedicated first driver circuit for controlling the CFL and a dedicated second driver circuit for controlling the LED. The CFL requires a high voltage, AC source and the first driver circuit or ballast associated therewith is an area of continued development and improvement. The LED, on the other hand, usually requires a DC power source and a low voltage. Thus, although combining the different types of light sources in a single lamp assembly is advantageous for light output, the combination presents unique issues since the needed driver circuits are so different. As will be appreciated, separate driver circuits add undesired cost and complexity to the lamp assembly.
Still another consideration is the space requirement of the lamp assembly. It is difficult to include separate LED and CFL driving circuits in the limited volume associated with the lamp assembly. Likewise, if the driving circuits are combined, then the same concerns with space requirements still exist.
There are several ways of driving a LED from a line-AC source. For example, one proposal uses a transformer for low voltage driving, and a resistor or capacitor for current limiting, that is before or after the transformer. Another option is to employ a current generator circuit using a switching power supply with a current limiter or generator. The switching power supply is connected with several LEDs. The current is limited by a capacitor and/or resistor.
One proposed solution to an integrated or combined circuit is disclosed in published international application WO2007/066252 A1. An LED circuit is connected in series with the fluorescent lamp and the high frequency alternating current that drives the fluorescent light source is supplied to the LED circuits. Each LED circuit has at least three parallel branches, namely, a first branch includes an impedance circuit while the second and third branches contain the LEDs which are connected in anti-parallel relation. The impedance circuit controls the amount of current flowing through one of the second and third branches at any one time (i.e., if there is high impedance, then a large part of the AC flows through the second or third branches, and vice versa if there is low impedance, then a small portion of the AC current flows through the second and third branches). Since the LED allows current to flow in only one direction, and the LEDs are arranged in anti-parallel relation in the second and third branches, the alternating current can flow through one of the second and third branches at any one time.
This solution is not as desirable since the LED and the fluorescent lamp are connected in series. Since, as noted above, an individual LED is usually driven by DC current, and fluorescent lamps are driven by AC current, the combined lamp assembly necessarily requires at least two LEDs—one operable in each current direction, Moreover, since the components are arranged in series relation, the current that flows through the fluorescent lamp and the LED driver circuit is necessarily the same. Further, ignition of the fluorescent lamp requires high voltage (on the order of 100 volts, for example, for a compact fluorescent lamp assembly). This voltage level is not desired for LEDs since it could potentially damage the LED light source.
Thus, a need exists for an inexpensive, compact, low power, efficient combined light assembly and associated combined driver circuit that addresses the competing, disparate requirements of the different types of light sources and overcomes the deficiencies identified above.